Generally, transmission errors occur more frequently in a radio communication system than in a wireline communication system. To ensure reliability in communication in such a radio communication system, hybrid automatic repeat request (HARQ) in which both of automatic repeat request (ARQ) and forward error correction (FEC) are used is widely employed in recent years.
In HARQ, in a case where a reception-side radio communication device (called reception device below) fails to decode data received from a transmission-side radio communication device (called transmission device below), the reception device transmits a retransmission request to the transmission device. Upon receipt of the retransmission request, the transmission device transmits the already-transmitted transmission data (initial transmission data) as retransmission data to the reception device.
The reception device stores the transmission data for which decoding had failed, and upon receipt of the retransmission data from the transmission device, combines the stored transmission data with the received retransmission data and decodes the resultant data. This leads to improvement in the error correction capability. The transmission device and reception device thus store transmission data until HARQ retransmission processing is completed.
Moreover, in a case where a transmission device such as a radio base station communicates with multiple reception devices such as radio terminals, the transmission device is provided with a scheduler which controls allocation of a radio resource such as time or frequencies to the multiple reception devices, according to receiving quality (a received SNR, for example) of each of the reception devices. Normally, the scheduler sets a high allocation priority (called priority below) for a reception device of high receiving quality, so that data can be transmitted by preferentially using a radio resource of high receiving quality. Hence, radio resource is utilized effectively and throughput is improved.
In a case where the aforementioned HARQ is applied to a transmission device including such a scheduler, for reduction of the amount of stored transmission data and retransmission delay, the transmission device generally transmits retransmission data with first priority regardless of priorities set by the scheduler (refer to Patent Document 1, for example).
Patent Document 1: Japanese Patent Application Publication No. 2005-39726 (see paragraphs [0028], [0029] and the like)